C++ getting number of data in an array? [duplicate] - c++

Question

This question already has answers here:
Find the count of elements in array in C++
(3 answers)
Closed 5 years ago.
I have a simple array here:
int someNumbers[10] = { 16, 2, 77, 40, 12071 };
How can I get the number of data inside the array? As the array was set to 10, but there is only 5 data inside.
My desired outcome should be something like this:
int icount = sizeof(someNumbers); // This is wrong, but I have no idea how..
cout << icount << endl;
I need icount to return 5 instead of 10. How can I do that?

Answer 1

This will do:
#include<iostream>
using namespace std;
int main(){
int someNumbers[10] = { 16, 2, 77, 40, 12071 };
int count = 0;
int i = 0;
for(i = 0; i < sizeof(someNumbers) / sizeof(int); i++){
if(someNumbers[i]){
count = count + 1;
}
}
cout << count << endl;
return 0;
}
I am using if(someNumber[i]) alone because this will return true as long as someNumber[i] is not undefined. Therefore, this works.
This is the output:
5
You can always make this a separate function like this:
#include<iostream>
using namespace std;
int dataInArray(int someNumbers[], int size);
int main(){
int someNumbers[10] = { 16, 2, 77, 40, 12071, 2};
int count = dataInArray(someNumbers, 10);
cout << count << endl;
return 0;
}
int dataInArray(int someNumbers[], int size){
int count = 0;
int i = 0;
for(i = 0; i < size; i++){
if(someNumbers[i]){
count = count + 1;
}
}
return count;
}

Answer 2

Since you are using a static array where the size is predefined, you would have to use a for loop to run through your array. See example here:
int someNumbers[10] = { 16, 2, 77, 40, 12071 };
int icount = 0;
for (int i = 0; i < 10; i++)
{
if (someNumbers[i])
icount++;
}
cout << icount << endl;
A bit of background information. If one of the memory blocks assigned to this array is not set by the user, it will store an empty value. Therefore, if we do if(isNumber[i]) then it will return true if someNumber at iis filled with a value, and it will return false if not filled with a value.
That is how the for-loop works in the code I posted. For every run of the loop, when the if statement is true, (if someNumber[i] has a value), then the counter is incremented.
EDIT: This solution works fine; for your array, it will output 5. It also works for any int array; just change the counter to run while it less than the static size you assign for the array.
EDIT 2: this solution works as long as there is no zero in your array, because a zero will falsify the if-condition. See more in this stackoverflow post: Find the count of elements in array in C++. To overcome this obstacle, it is recommended that you use std::vector, or use a counter variable and update the exact number of memory locations in the array that are filled in this variable manually.

Answer 3

What you are asking for just is not possible, because according to the language rules, there is no difference at all between:
int someNumbers[10] = { 16, 2, 77, 40, 12071 };
and
int someNumbers[10] = { 16, 2, 77, 40, 12071, 0, 0, 0, 0, 0 };
Both of them definitely initialize all ten elements.
If you're interested in finding the first zero (whether it was typed by the programmer or implied by the language rules) then #ABusyProgrammer's answer will help.
If you need to count zeros which the programmer typed, then you have to let the compiler infer the array (or initializer_list, as mentioned in comments) length from the initializer as #Kelm's answer shows.
There's no way to both detect zeros typed by the programmer and also specify the array size.

Answer 4

Use this:
int someNumbers[] = { 16, 2, 77, 40, 12071 };
cout << sizeof(someNumbers)/sizeof(int) <<endl;
This is because sizeof(someNumbers) does not give you the count of the array but rather the total number of bytes it is taking. So divide it by sizeof(int) and it will give you the number of integers in the array.
Also, if you specify [10] while declaring the array then the count of the array will be 10, regardless of whether it is initialized with fewer values. The way shown above, with an empty [], it will automatic set the count according to the number of elements specified.
ideone link

Answer 5

This should do it:
int someNumbers[] = {1,2,3,4,5,6};
int icount = sizeof(someNumbers) / sizeof(int);